It is well known that the enzymatic action of glucose oxidase is antibacterial. In the presence of oxygen, glucose oxidase catalyzes the oxidation of glucose to .differential.-gluconolactone and hydrogen peroxide. The antibacterial mode of action is due to both the oxidative potential of hydrogen peroxide as well as the presence of the .differential.-gluconolactone, which is a known glycosyltransferase inhibitor.
The antibacterial effect of the products of this enzyme has resulted in its wide-spread use in the food industry, where it is considered a GRAS [generally recognized as safe] compound. As such, glucose oxidase is used to prevent bacterial spoilage of prepared foods. In medicine, it is used as an enzymatic bactericide as part of a preparation for use in wound dressings, toothpicks, dental floss and miniature tooth-brushes. Glucose oxidase has also been mentioned as a method to control dental caries.
Recent reports have shown that a glucose oxidase is involved as part of the bio-control mechanism used by Penicillium dangearii to control the plant pathogenic fungus Verticillium dahliae. [Kim et al., 1988, 1990].
However, the use of glucose oxidase as a means for plants to protect themselves from pathogenic organisms has been thought to have little potential due to the nature of the enzymatic action. First, there is little free glucose present in plants. The enzyme would seem to have insufficient substrate to produce enough hydrogen peroxide and/or .differential.-gluconolactone to overcome a pathogenic attack. Second, the presence of such an enzyme in a plant cell, consuming glucose and producing even a small amount of hydrogen peroxide, would be expected to be detrimental to the vitality of the cell. Transgenic plants expressing glucose oxidase would not be expected to develop normally, either as regenerated plants or in subsequent generations.
It is an object of the present invention to provide a glucose oxidase that can be safely expressed in plant cells and provide disease resistance to those cells. It is a further object of the present invention to provide a method of transforming plants to express a glucose oxidase which can be safely expressed in plants and provide disease resistance to those plants.